The present invention relates in general to methods and apparatus for constructing tunnels.
It is known to produce a tunnel with the aid of a shield advanced by rams and to provide a support lining for the tunnel wall by introducing fluid concrete behind the shield. In the related U.S. Pat. Nos. 3,834,170 and 3,889,480, assigned to the same assignee as the present invention, there is generally disclosed an apparatus of the aforementioned type wherein water is driven out from the fluid concrete through filters when the rams are operated to advance the shield by making the rams compress the concrete. In some cases it may be more desirable to expel water from the concrete prior to advancement of the shield, i.e., independently of the operation of the rams and to effect better control of the water extracting operation.
With this in mind the present invention seeks to provide an improved apparatus and methods.